Endoscope system and light source device

ABSTRACT

Violet narrowband light Vn and green narrowband light Gn produced by a light source device are supplied to a complementary color type endoscope, and simultaneously applied to an observation object. In a complementary color type imaging device, first mixed pixels and second mixed pixels, which sense both of the violet narrowband light Vn and the green narrowband light Gn, are read out. The light amount ratio Z of the violet narrowband light Vn to the green narrowband light Gn is set in such a range as to make the light amount of the violet narrowband light Vn larger than the light amount of the green narrowband light Gn, and make a signal value of the second mixed pixel higher than a signal value of the first mixed pixel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of copending application Ser. No.14/338,988, filed on Jul. 23, 2014, which claims priority under 35 U.S.C§119 to Japanese Patent Application No. 2013-202553 filed on Sep. 27,2013. The above applications are hereby expressly incorporated byreference, in their entireties, into the present application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an endoscope system for performingnarrowband light observation using a complementary color type imagingdevice, and a light source device used in the endoscope system.

2. Description Related to the Prior Art

In a recent medical field, diagnosis and treatment using an endoscopesystem, having a light source device, an electronic endoscope, and aprocessor device, are widely performed. The light source device producesillumination light and applies the illumination light to the inside of ahuman body cavity. The electronic endoscope images the inside of thebody cavity irradiated with the illumination light by an imaging device,and produces an imaging signal. The processor device applies imageprocessing to the imaging signal produced by the electronic endoscope toproduce an observation image to be displayed on a monitor.

As an observation method used in the endoscope system, there is knownnarrowband light observation using special light (narrowband light)having a narrow wavelength band as the illumination light, in additionto normal light observation using normal light (white light) having awide wavelength band as the illumination light. The narrowband lightobservation, for example, can improve visibility of a blood vesselpattern in a superficial layer of a mucosa membrane, though the bloodvessel pattern is easily buried in optical information obtained underirradiation with the white light. Therefore, the narrowband lightobservation allows focusing attention on superficial blood vessels ofthe blood vessel pattern, and diagnosing the stage of a disease, thedepth of a lesion, and the like from the state of the superficial bloodvessels.

The narrowband light observation uses two types of narrowband lightabsorbable by hemoglobin in blood, that is, blue narrowband light havinga center wavelength in the vicinity of 415 nm and green narrowband lighthaving a center wavelength in the vicinity of 540 nm. As an imagingmethod in the narrowband light observation, there are known a framesequential method in which the blue narrowband light and the greennarrowband light are alternately applied and a monochrome imaging devicecaptures an image whenever each type of light is applied, and asimultaneous method in which the blue narrowband light and the greennarrowband light are simultaneously applied and a simultaneous imagingdevice having color filters captures an image (see U.S. Pat. No.8,531,512 and US Patent Application Publication No. 2009/0141125). Thesimultaneous method is inferior in resolution to the frame sequentialmethod, but has the advantages of preventing a blur in the image andstructural simplicity of the endoscope system.

The simultaneous imaging device includes a primary color type imagingdevice having primary color filters and a complementary color typeimaging device having complementary color filters. The primary colortype imaging device is used in an endoscope system that placesimportance on color, because of being superior in color reproducibility,though inferior in sensitivity, to the complementary color type imagingdevice. On the other hand, the complementary color type imaging device,which is superior in sensitivity and inferior in color reproducibilityto the primary color type imaging device, is used in an endoscope systemthat places importance on sensitivity. Since the primary color typeimaging device and the complementary color type imaging device have bothadvantage and disadvantage, it is desired that an endoscope system ofthe future be available with both of a primary color type endoscopecontaining the primary color type imaging device and a complementarycolor type endoscope containing the complementary color type imagingdevice.

The U.S. Pat. No. 8,531,512 and the US Patent Application PublicationNo. 2009/0141125 disclose a complementary color type imaging device of acomplementary-color checkered-pattern color-difference line sequentialmethod having four types of pixels of magenta (Mg), green (G), cyan(Cy), and yellow (Ye). According to the complementary-colorcheckered-pattern color-difference line sequential method, pixel signalsare read out by a field readout method in a state of mixing (adding) thepixel signals of two adjoining rows. More specifically, the pixelsignals are read out in a state of four types of combinations, i.e. theMg pixel and the Cy pixel, the G pixel and the Ye pixel, the Mg pixeland the Ye pixel, and the G pixel and the Cy pixel. Thecomplementary-color checkered-pattern color-difference line sequentialmethod has the advantage of ease of producing a Y/C signal and an RGBsignal just by addition and subtraction of the signals of the four typesof mixed pixels.

In the case of performing the narrowband light observation by theendoscope system described above, according to the primary color typeimaging device, blue (B) pixels capture the blue narrowband light andgreen (G) pixels capture the green narrowband light, independently.Thus, the primary color type imaging device can produce an image thathas high color separability and high visibility of the superficial bloodvessels (high contrast between the superficial blood vessels and themucosa membrane). On the contrary, in the complementary color typeimaging device, each mixed pixel senses the blue narrowband light andthe green narrowband light at the same time (i.e. mixture of colorsoccurs). This causes low color separability, and a blur of thesuperficial blood vessels due to the influence of scattered lightdeteriorates the visibility of the superficial blood vessels.

In relation to this problem, the U.S. Pat. No. 8,531,512 and the USPatent Application Publication No. 2009/0141125 describe that changingcoefficients of a matrix operation for converting a Y/C signal into anRGB signal in accordance with characteristics and the like of colorfilters reduces color mixture. However, this matrix operation isperformed in a signal processing circuit that performs an operation ofmixed pixel signals, and each of the mixed pixel signals is a signal inwhich a blue narrowband light component and a green narrowband lightcomponent have already been mixed at the time of entering the signalprocessing circuit. Therefore, the matrix operation cannot radicallyimprove the color separability and the visibility of the superficialblood vessels.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an endoscope system anda light source device that allow improvement in color separability andvisibility of superficial blood vessels in narrowband light observationusing a complementary color type imaging device.

To achieve the above and other objects, an endoscope system according tothe present invention includes a complementary color type imagingdevice, a signal processing unit, and a lighting section. A first mixedpixel and a second mixed pixel, which sense both of first narrowbandlight and second narrowband light having a longer wavelength than thefirst narrowband light, are read out from the complementary color typeimaging device. The signal processing unit images the first narrowbandlight by using a signal value of the first mixed pixel, and images thesecond narrowband light by using a signal value of the second mixedpixel. The lighting section has a light source device for simultaneouslyapplying the first and second narrowband light to an observation object.In the light source device, the light amount ratio between the firstnarrowband light and the second narrowband light is set such that thelight amount of the first narrowband light is made larger than the lightamount of the second narrowband light and the signal value of the secondmixed pixel is made higher than the signal value of the first mixedpixel.

The complementary color type imaging device preferably has a matrix ofat least four types of pixels for performing photoelectric conversion oflight of different colors. Two types of the four types of pixels next toin a vertical scan direction compose the first mixed pixel. Other twotypes of the four types of pixels next to in the vertical scan directioncompose the second mixed pixel.

The light amount ratio is preferably set at a value “Z” satisfying thefollowing expression (a):

$\begin{matrix}{1 < Z < {Z_{i}\frac{S_{2}}{S_{1}}}} & (a)\end{matrix}$wherein, S₁ represents the signal value of the first mixed pixel byindependent application of only the first narrowband light, and S₂represents the signal value of the second mixed pixel by independentapplication of only the second narrowband light, and Z_(i) representsthe light amount ratio of the first narrowband light to the secondnarrowband light in the independent application.

It is preferable that S₁ be an average of the signal values of aplurality of first mixed pixels by independent application of only thefirst narrowband light, and S₂ be an average of the signal values of aplurality of second mixed pixels by independent application of only thesecond narrowband light.

It is preferable that a complementary color type endoscope having thecomplementary color type imaging device and a primary color typeendoscope having a primary color type imaging device be detachablyconnected to the light source device.

The endoscope system preferably includes a controller for controllingthe light source device, such that the light amount ratio is set at alarger value in a case where the complementary color type endoscope isconnected to the light source device than in a case where the primarycolor type endoscope is connected to the light source device.

The controller preferably sets the light amount ratio at “1” in a casewhere the primary color type endoscope is connected to the light sourcedevice, while the controller sets the light amount ratio at “Z”satisfying the expression (a) in a case where the complementary colortype endoscope is connected to the light source device.

Each of the complementary color type endoscope and the primary colortype endoscope preferably has information storage for storing specificinformation, and the controller preferably reads out the specificinformation from the information storage of the complementary color typeendoscope or the primary color type endoscope that is connected to thelight source device in order to judge the type of the connectedendoscope.

The information storage of the complementary color type endoscopepreferably stores an optimal light amount ratio satisfying theexpression (a). In a case where the complementary color type endoscopeis connected to the light source device, the controller determines thelight amount ratio on the basis of the optimal light amount ratio readout of the information storage.

The endoscope system preferably has a calibration mode for calculatingthe optimal light amount ratio with applying the first and secondnarrowband light independently from the light source device. Thecontroller preferably stores the optimal light amount ratio calculatedin the calibration mode to the information storage of the complementarycolor type endoscope connected to the light source device.

The light source device preferably includes a plurality of LEDs. Thecontroller preferably sets the light amount ratio by regulating at leastone of light emission intensity and light emission time of the pluralityof LEDs.

The endoscope system preferably includes a corrector for correcting asignal value M1 of the first mixed pixel and a signal value M2 of thesecond mixed pixel on the basis of the following expressions (b) and(c):M1′=M1−K ₂ ×M2  (b)M2′=M2−K ₁ ×M1  (c)wherein, K₁ represents the ratio of the signal value of the second mixedpixel to the signal value of the first mixed pixel by independentapplication of only the first narrowband light, K₂ represents the ratioof the signal value of the first mixed pixel to the signal value of thesecond mixed pixel by independent application of only the secondnarrowband light.

Each of the four types of pixels preferably has one of color filtersegments of cyan, magenta, yellow, and green arranged in a checkeredpattern. The first mixed pixel is preferably a combination of a magentapixel and a cyan pixel, and the second mixed pixel is preferably acombination of a green pixel and a yellow pixel. The first narrowbandlight preferably has a center wavelength in a blue or violet wavelengthregion, and the second narrowband light preferably has a centerwavelength in a green wavelength region.

The endoscope system preferably includes a channel allocator forassigning the signal value of the first mixed pixel to a B channel and aG channel of an image display device, and assigning the signal value ofthe second mixed pixel to an R channel of the image display device, todisplay a special image.

The light amount ratio is preferably set at a value “Z” satisfying thefollowing expression (d):

$\begin{matrix}{1 < Z < \frac{a_{2}}{a_{1}}} & (d)\end{matrix}$wherein, a₁ represents sensitivity of the first mixed pixel to the firstnarrowband light, and a₂ represents sensitivity of the second mixedpixel to the second narrowband light.

A light source device according to the present invention includes alight source and a light source controller for controlling the lightsource. The light source simultaneously produces first narrowband lightand second narrowband light having a longer wavelength than the firstnarrowband light, and supplies the first and second narrowband light toan endoscope. A complementary color type imaging device from which afirst mixed pixel and a second mixed pixel are read out is connectableto the light source device, and the first mixed pixel and the secondmixed pixel sense both of the first narrowband light and the secondnarrowband light. The light source device simultaneously applies thefirst and second narrowband light to an observation object. The lightsource device sets the light amount ratio between the first narrowbandlight and the second narrowband light, such that the light amount of thefirst narrowband light is made larger than the light amount of thesecond narrowband light and the signal value of the second mixed pixelis made higher than the signal value of the first mixed pixel.

According to the present invention, the light amount ratio of the firstnarrowband light to the second narrowband light is determined such thatthe light amount of the first narrowband light is made larger than thelight amount of the second narrowband light and the signal value of thesecond mixed pixel is made higher than the signal value of the firstmixed pixel. Therefore, it is possible to improve the color separabilityand the visibility of the superficial blood vessels.

BRIEF DESCRIPTION OF DRAWINGS

For more complete understanding of the present invention, and theadvantage thereof, reference is now made to the subsequent descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view of an endoscope system;

FIG. 2 is a block diagram of the endoscope system;

FIG. 3 is a graph showing an emission spectrum of violet narrowbandlight;

FIG. 4 is a graph showing an emission spectrum of normal light;

FIG. 5 is an explanatory view of the structure of an optical combiner;

FIG. 6 is a graph showing an emission spectrum of green narrowbandlight;

FIG. 7 is a schematic view of a complementary color type colorseparation filter;

FIG. 8 is a schematic view of a primary color type color separationfilter;

FIG. 9 is a timing chart of light sources and a complementary color typeimaging device in a narrowband light observation mode;

FIG. 10 is an explanatory view of output signals from the complementarycolor type imaging device;

FIG. 11 is a graph of spectral sensitivity characteristics of thecomplementary color type imaging device;

FIG. 12 is a graph of spectral sensitivity characteristics of first tofourth mixed pixels;

FIG. 13 is a graph of a spectral attenuation characteristic of a lightguide;

FIG. 14 is a timing chart of the light sources and the complementarycolor type imaging device in a calibration mode;

FIG. 15 is a block diagram of a complementary color first processor;

FIG. 16 is a graph showing the rate of a main component of each of firstand second mixed pixel signals and the sum of the rates;

FIG. 17 is a flowchart of the operation of the endoscope system;

FIG. 18 is a graph showing an emission spectrum of blue narrowbandlight;

FIG. 19 is a schematic view of a modification example of a light sourcedevice;

FIG. 20 is a schematic view of a rotary filter unit;

FIG. 21 is a graph showing a transmission characteristic of a firstnarrowband filter;

FIG. 22 is a graph showing a transmission characteristic of a secondnarrowband filter; and

FIG. 23 is a schematic view of a modification example of thecomplementary color type color separation filter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, an endoscope system 10 is constituted of a light sourcedevice 11, a processor device 12, and electronic endoscopes 13(hereinafter simply called endoscopes) detachably connected to the lightsource device 11 and the processor device 12. The light source device 11produces illumination light and supplies the endoscope 13 with theillumination light. A distal end of the endoscope 13 is inserted into ahuman body cavity or the like to image the inside of the body cavity.The processor device 12 controls the imaging operation of the endoscope13, and applies signal processing to an imaging signal obtained by theendoscope 13.

To the processor device 12, an image display device 14 and an inputdevice 15 are connected. The image display device 14, being a liquidcrystal display or the like, displays an image of an observation objectinside the body cavity produced by the processor device 12. The inputdevice 15, including a keyboard and a mouse, is used for inputtingvarious types of information to the processor device 12.

The endoscopes 13 include a complementary color type endoscope 13 ahaving a complementary color type imaging device 28 (see FIG. 2) and aprimary color type endoscope 13 b having a primary color type imagingdevice 29 (see FIG. 2). Either of the complementary color type endoscope13 a and the primary color type endoscope 13 b is connectable to thelight source device 11 and the processor device 12. The complementarycolor type endoscope 13 a and the primary color type endoscope 13 b haveidentical structure except for the imaging device. Each endoscope 13 aor 13 b includes an insert section 16, a control handle unit 17, auniversal cable 18, a light guide connector 19 a, and a signal connector19 b.

The slender insert section 16 is introduced into the human body cavityor the like. The control handle unit 17 is coupled to a rear end of theinsert section 16. The control handle unit 17 is provided with variousswitches, a bending operation dial, and the like. The various switchesinclude a mode switch 17 a for switching an operation mode.

The universal cable 18 extends from the control handle unit 17. Thelight guide connector 19 a and the signal connector 19 b are attached toan end of the universal cable 18. The light guide connector 19 a isdetachably connected to the light source device 11. The signal connector19 b is detachably connected to the processor device 12.

As an observation mode of the endoscope system 10, there are provided anormal light observation mode and a narrowband light observation mode.In the normal light observation mode, the observation object is imagedunder irradiation with normal light (white light) having a wavelengthband extending from the blue region to the red region, and a normalimage is produced. In the narrowband light observation mode, theobservation object is imaged under irradiation with narrowband light(violet narrowband light Vn and green narrowband light Gn, describedlater on) having a narrow wavelength band, and a narrowband light imageis produced. Both of the complementary color type endoscope 13 a and theprimary color type endoscope 13 b can carry out the normal lightobservation mode and the narrowband light observation mode.

The endoscope system 10 is switchable between the normal lightobservation mode and the narrowband light observation mode by operationof the mode switch 17 a described above, but may be switched byoperation of a foot switch (not shown) connected to the processor device12, a button provided on a front panel of the processor device 12, theinput device 15, or the like.

In FIG. 2, the light source device 11 has an LED (light emitting diode)light source 20, a light source controller 21, and an optical combiner24. The LED light source 20 includes a violet LED (V-LED) 20 a and awhite LED (WL-LED) 20 b. Referring to FIG. 3, the V-LED 20 a producesviolet narrowband light Vn having a wavelength band of 380 to 440 nm.Referring to FIG. 4, the WL-LED 20 b produces white light WL of a widewavelength band. The light source controller 21 controls light emissionfrom the V-LED 20 a and the WL-LED 20 b.

As shown in FIG. 5, the optical combiner 24 has a dichroic mirror 22 andfirst to third lenses 23 a to 23 c. The first lens 23 a is disposed infront of the LED 20 a, and gathers and collimates the light emitted fromthe LED 20 a. The second lens 23 b is disposed in front of the LED 20 b,and gathers and collimates the light emitted from the LED 20 b. TheV-LED 20 a and the WL-LED 20 b are disposed such that optical axes ofthe V-LED 20 a and the WL-LED 20 b are orthogonal to each other. Thedichroic mirror 22 is situated at an intersection point of the opticalaxes.

The dichroic mirror 22 transmits light in a wavelength band of 530 nm ormore and less than 550 nm, and reflects light in a wavelength of lessthan 530 nm or 550 nm or more, for example. Thus, the violet narrowbandlight Vn is reflected by the dichroic mirror 22 and gathered by thethird lens 23 c. On the other hand, a part of the white light WL ispassed through the dichroic mirror 22, and gathered by the third lens 23c as green narrowband light Gn having a wavelength band of 530 to 550nm, as shown in FIG. 6.

In the narrowband light observation mode, the V-LED 20 a and the WL-LED20 b are simultaneously turned on. The violet narrowband light Vn andthe green narrowband light Gn are combined (mixed) by the dichroicmirror 22 and gathered by the third lens 23 c, and enter a light guide27.

In the normal light observation mode, a shift mechanism (not shown)moves the dichroic mirror 22 out of the optical axis of the WL-LED 20 b.Thus, in the normal light observation mode, the white light WL isdirectly incident upon the third lens 23 c, and led into the light guide27. Since the dichroic mirror 22 is retracted in the normal lightobservation mode, the violet narrowband light Vn emitted from the V-LED20 a is not incident upon the third lens 23 c even if the dichroicmirror 22 reflects the violet narrowband light Vn. Thus, the V-LED 20 ais preferably turned off, but there is no harm in turning on the V-LED20 a.

The center wavelength of the violet narrowband light Vn is approximately405 nm at which hemoglobin has a high absorption coefficient in thevisible region. The center wavelength of the green narrowband light Gnis approximately 540 nm at which hemoglobin has a high absorptioncoefficient in the green wavelength region. The green narrowband lightGn has a higher reflectance from a mucosa membrane than the violetnarrowband light Vn.

The insert section 16 of the endoscope 13 has at its tip end a lightingwindow and an image capturing window provided next to each other. Alighting lens 25 is fitted into the lighting window. An objective lens26 is fitted into the image capturing window. The light guide 27 extendsthrough the endoscope 13, and one end of the light guide 27 is opposedto the lighting lens 25. The other end of the light guide 27 is providedwith the light guide connector 19 a. In a state of fitting the lightguide connector 19 a to the light source device 11, the other end of thelight guide 27 is inserted into the light source device 11.

The lighting lens 25 gathers the light that is transmitted from thelight source device 11 through the light guide 27 and ejected from thelight guide 27, and applies the light to the observation object insidethe body cavity. The objective lens 26 gathers reflected light fromliving body tissue and the like of the observation object, and forms anoptical image. In an image forming position of the objective lens 26, animaging device (the complementary color type imaging device 28 in thecase of the complementary color type endoscope 13 a, the primary colortype imaging device 29 in the case of the primary color type endoscope13 b) is disposed to capture the optical image and produce the imagingsignal. The complementary color type imaging device 28 and the primarycolor type imaging device 29 are CCD (charge coupled device) imagesensors.

The complementary color type imaging device 28 is provided at itsimaging surface with a complementary color type color separation filter28 a to perform optical color separation of the optical image on apixel-by-pixel basis. As shown in FIG. 7, this complementary color typecolor separation filter 28 a has four types of color filter segments ofmagenta (Mg), green (G), cyan (Cy), and yellow (Ye), and one colorfilter segment is provided for each pixel. Accordingly, thecomplementary color type imaging device 28 has four types of pixels ofMg, G, Cy, and Ye. The Mg pixels and the G pixels are alternatelyarranged in odd-number rows, and the Cy pixels and the Ye pixels arealternately arranged in even-number rows, such that the Mg pixel, the Cypixel, the Mg pixel, the Ye pixel, . . . are arranged in this order inodd-number columns, and the G pixel, the Ye pixel, the G pixel, the Cypixel . . . are arranged in this order in even-number columns. Thiscolor filter pattern is referred to as a complementary-colorcheckered-pattern color-difference line sequential method. A rowdirection refers to a horizontal scan direction, and a column directionrefers to a vertical scan direction.

The primary color type imaging device 29 is provided at its imagingsurface with a primary color type color separation filter 29 a. As shownin FIG. 8, this primary color type color separation filter 29 a hasthree types of color filter segments of red (R), green (G), and blue(B), which are three primary colors of an additive color process. Onecolor filter segment is provided for each pixel. Accordingly, theprimary color type imaging device 29 has three types of pixels of R, G,and B. The G pixels and the B pixels are alternately arranged inodd-number columns, and the R pixels and the G pixels are alternatelyarranged in even-number columns. The G pixels and the R pixels arealternately arranged in odd-number rows, and the B pixels and the Gpixels are alternately arranged in even-number rows. This color filterpattern is referred to as a primary color Bayer pattern.

The endoscope 13 includes information storage 30 composed of anon-volatile memory such as a flash memory. The information storage 30stores specific information (the color filter pattern and the pixelnumber of the imaging device) and the like of the endoscope 13.

The processor device 12 has a main controller 31, an imaging controller32, a correlated double sampling (CDS) circuit 33, an A/D converter 34,a brightness detector 35, a dimmer 36, a signal processing unit 37, anda channel allocator 38.

The main controller 31 controls each part of the processor device 12 andthe light source device 11. Upon connecting the endoscope 13 to thelight source device 11 and the processor device 12, the main controller31 reads the specific information of the endoscope 13 from theinformation storage 30, and judges whether the connected endoscope 13 isthe complementary color type endoscope 13 a or the primary color typeendoscope 13 b. The imaging controller 32 actuates the imaging device(complementary color type imaging device 28 or the primary color typeimaging device 29) in accordance with the type of the endoscope 13judged by the main controller 31.

In the case of the complementary color type imaging device 28, theimaging controller 32 drives the complementary color type imaging device28 by a field readout method in synchronization with emission timing ofthe light source device 11. To be more specific, according to the fieldreadout method, pixel signals of two pixels adjoining in the columndirection (vertical scan direction) are read out in a mixed (added)manner in reading each of an odd-number field and an even-number field(see FIG. 7). The mixture of the pixel signals is performed in ahorizontal transfer path (not shown) of the CCD image sensor by usingthe pixel signals of two rows. FIG. 9 shows a timing chart of thenarrowband light observation mode. A timing chart of the normal lightobservation mode is the same as that of the narrowband light observationmode, except that the illumination light is the white light WL.

According to the field readout method, as shown in FIG. 10, a mixedpixel signal (hereinafter called a first mixed pixel signal) M1 of theMg pixel and the Cy pixel, a mixed pixel signal (hereinafter called asecond mixed pixel signal) M2 of the G pixel and the Ye pixel, a mixedpixel signal (hereinafter called a third mixed pixel signal) M3 of theMg pixel and the Ye pixel, and a mixed pixel signal (hereinafter calleda fourth mixed pixel signal) M4 of the G pixel and the Cy pixel are readout from the complementary color type imaging device 28 in each of theodd-number field and the even-number field.

Since the pixels of the complementary color type imaging device 28 havespectral sensitivity characteristics as shown in FIG. 11, for example,in accordance with the color filter segments provided thereto, the mixedpixels have spectral sensitivity characteristics as shown in FIG. 12,for example. As is apparent from the spectral sensitivitycharacteristics, out of the first to fourth mixed pixels, the firstmixed pixel (Mg+Cy) is the most sensitive to the violet narrowband lightVn (a center wavelength of 405 nm), and the second mixed pixel (G+Ye) isthe most sensitive to the green narrowband light Gn (a center wavelengthof 540 nm). However, the first mixed pixel (Mg+Cy) has high sensitivityto the green narrowband light Gn too. The second mixed pixel (G+Ye) hasa little sensitivity to the violet narrowband light Vn.

In the narrowband light observation mode, the violet narrowband light Vnis imaged based on the first mixed pixel signal M1, and the greennarrowband light Gn is imaged based on the second mixed pixel signal M2.On the other hand, in the normal light observation mode, imaging isperformed by using all of the first to fourth mixed pixel signals M1 toM4.

In the case of the primary color type imaging device 29, the imagingcontroller 32 drives the primary color type imaging device 29 by awell-known progressive readout method in synchronization with emissiontiming of the light source device 11. According to the progressivereadout method, the pixel signals of one frame are read out sequentiallyand individually on a row-by-row basis, without mixing the pixelsignals.

A signal outputted from the complementary color type imaging device 28or the primary color type imaging device 29 is inputted to the CDScircuit 33. The CDS circuit 33 applies correlated double sampling to theinputted signal to remove a noise component occurring in the CCD imagesensor. The signal, after the noise removal by the CDS circuit 33, isinputted to the A/D converter 34 and the brightness detector 35. The A/Dconverter 34 converts the signal inputted from the CDS circuit 33 into adigital signal, and inputs the digital signal to the signal processingunit 37.

The brightness detector 35 detects as brightness (average luminance ofthe signal) an average value of G signals, in general, based on thesignal inputted from the CDS circuit 33. The dimmer 36 produces adimming signal, which represents the difference between a brightnesssignal detected by the brightness detector 35 and standard brightness (atarget dimming value). This dimming signal is inputted to the lightsource controller 21. The light source controller 21 adjusts the lightemission amount of the LED light source 20 so as to obtain the standardbrightness.

Upon receiving a mode switching signal issued by the operation of themode switch 17 a of the endoscope 13, the main controller 31 switches alight emission method of the light source device 11 and a signalprocessing method of the signal processing unit 37 in accordance withthe received mode switching signal.

In the narrowband light observation mode, the main controller 31controls the light source controller 21 in accordance with the type ofthe endoscope 13 defined by the specific information read out of theinformation storage 30 so as to change the light emission intensity ofthe V-LED 20 a and the WL-LED 20 b. More specifically, in the case ofthe primary color type endoscope 13 b, the main controller 31 controlsthe light source controller 21 so as to substantially equalize the lightamounts of the violet narrowband light Vn and the green narrowband lightGn applied from the primary color type endoscope 13 b to the observationobject.

On the other hand, in the case of the complementary color type endoscope13 a, the main controller 31 controls the light source controller 21such that the light amount ratio Z of the light amount X of the violetnarrowband light Vn to the light amount Y of the green narrowband lightGn applied from the complementary color type endoscope 13 a to theobservation object satisfies the following expression (1). This lightamount ratio Z (Z=X/Y) is at least larger than the light amount ratio(Z=1) in the case of the primary color type endoscope 13 b.

$\begin{matrix}{1 < Z < {Z_{i}\frac{S_{2}}{S_{1}}}} & (1)\end{matrix}$

wherein, S₁ represents a first mixed pixel signal M1 v obtained in thecase of independently applying only the violet narrowband light Vn. S₂represents a second mixed pixel signal M2 g obtained in the case ofindependently applying only the green narrowband light Gn. Z_(i)represents the ratio (X_(i)/Y_(i)) of the light amount X_(i) of theviolet narrowband light Vn to the light amount Y_(i) of the greennarrowband light Gn in the independent application.

The expression (1) corresponds to a condition of the light amount ratioZ for making the light amount X of the violet narrowband light Vn higherthan the light amount Y of the green narrowband light Gn that aresimultaneously applied to the observation object, and for making asignal value of the second mixed pixels used for imaging the greennarrowband light Gn higher than a signal value of the first mixed pixelsused for imaging the violet narrowband light Vn. Therefore, it ispossible to improve color separability and the visibility of superficialblood vessels (the contrast between the superficial blood vessels andthe mucosa membrane), as described later on.

Especially, the light amount ratio Z is preferably set at an optimallight amount ratio Z₀ represented by the following expression (2). Thisoptimal light amount ratio Z₀ is a median value of the confines definedby the expression (1).

$\begin{matrix}{Z_{0} = {\frac{1}{2}( {{Z_{i}\frac{S_{2}}{S_{1}}} + 1} )}} & (2)\end{matrix}$

It is preferable that S₁ be an average value of a plurality of firstmixed pixel signals M1 v in independent application of the violetnarrowband light Vn, (for example, an average value of all the firstmixed pixel signals M1 v in the odd-number field and the even-numberfield). Likewise, it is preferable that S₂ be an average value of aplurality of second mixed pixel signals M2 g in independent applicationof the green narrowband light Gn, (for example, an average value of allthe second mixed pixel signals M2 g in the odd-number field and theeven-number field).

To obtain this optimal light amount ratio Z₀, in a final test process orthe like in the course of manufacturing the endoscope system 10, theviolet narrowband light Vn and the green narrowband light Gn areindependently emitted (by time-sharing emission) from the light sourcedevice 11 at a predetermined light amount ratio Z_(i) (for example,Z_(i)=1), and the first and second mixed pixel signals M1 v and M2 g areobtained by the complementary color type imaging device 28, and theoptimal light amount ratio Z₀ is calculated from the expression (2). Theoptimal light amount ratio Z₀ obtained in the course of manufacturing isrecorded to the image storage 30 of the complementary color typeendoscope 13 a.

Provided that the complementary color type endoscope 13 a is connectedto the light source device 11 and the processor device 12 and thenarrowband light observation mode is chosen by operation of the modeswitch 17 a, the main controller 31 reads out the optimal light amountratio Z₀ stored in the information storage 30 of the complementary colortype endoscope 13 a. The main controller 31 controls the light sourcecontroller 21 to set the light emission intensity of the V-LED 20 a andthe WL-LED 20 b by intensity modulation, such that the complementarycolor type endoscope 13 a emits the violet narrowband light Vn and thegreen narrowband light Gn at the light amount ratio Z satisfying theexpression (1).

The above light guide 27 has a spectral attenuation characteristic asshown in FIG. 13. An attenuation factor of propagating light isincreased in a short wavelength range of approximately 440 nm or less.Thus, the violet narrowband light Vn emitted from the light sourcedevice 11 attenuates more strongly than the green narrowband light Gn inthe light guide 27 of the complementary color type endoscope 13 a. As aresult, since the light emission intensity ratio between the V-LED 20 aand the WL-LED 20 b does not coincide with the light amount ratio Zbetween the violet narrowband light Vn and the green narrowband light Gnemitted from the complimentary color type endoscope 13 a, the maincontroller 31 determines the light emission intensity of the V-LED 20 aand the WL-LED 20 b in consideration of the spectral attenuation factorof the light guide 27. For example, the relation between the lightemission intensity ratio of the V-LED 20 a and the WL-LED 20 b and thelight amount ratio Z of the violet narrowband light Vn and the greennarrowband light Gn emitted from the complementary color type endoscope13 a is measured in advance and put into a table. The V-LED 20 a and theWL-LED 20 b may be controlled based on this table.

The endoscope system 10 has a calibration mode for allowingrecalculation of the optimal light amount ratio Z₀ after the completionof the manufacture as a product. The calibration mode is chosen byoperation of the input device 15 or the like. In the calibration mode,the main controller 31 turns on the V-LED 20 a and the WL-LED 20 bindependently. Thus, as shown in FIG. 14, the violet narrowband light Vnand the green narrowband light Gn are applied in a time sharing manner,and the complementary color type imaging device 28 is driven insynchronization with emission timing.

In the calibration mode, the light amount ratio Z set in the lightsource controller 21 is used as the light amount ratio Z_(i) between theviolet narrowband light Vn and the green narrowband light Gn. The maincontroller 31 includes an optimal light amount ratio calculator 39. Theoptimal light amount ratio calculator 39 calculates the optimal lightamount ratio Z₀ by the expression (2).

The signal processing unit 37 includes a selector 40, a complementarycolor first processor 41, a complementary color second processor 42, aprimary color first processor 43, a primary color second processor 44,and a calibration processor 45. The selector 40 chooses one of theprocessors 41 to 45 in accordance with the type and the operation modeof the endoscope 13 judged by the main controller 31.

The calibration processor 45 is chosen in the above calibration mode. Inthe calibration mode, a signal outputted from the complementary colortype imaging device 28 is inputted to the signal processing unit 37through the CDS circuit 33 and the A/D converter 34, and sent to thecalibration processor 45 via the selector 40. The calibration processor45 extracts the above first and second mixed pixel signals M1 v and M2 gfrom the input signal. The calibration processor 45 calculates anaverage of signal values of each of the first and second mixed pixelsignals M1 v and M2 g, and inputs the averages to the optimal lightamount ratio calculator 39 of the main controller 31. The optimal lightamount ratio calculator 39 calculates the optimal light amount ratio Z₀from the expression (2) with the use of the signal values inputted fromthe calibration processor 45.

After performing the calibration, the main controller 31 deletes theoptimal light amount ratio Z₀ that has been stored in the informationstorage 30 of the complementary color type endoscope 13 a, and replacesit with the optimal light amount ratio Z₀ that is newly calculated bythe optimal light amount ratio calculator 39.

The complementary color first processor 41 is chosen in a case where theendoscope 13 is of the complementary color type and the observation modeis the normal light observation mode. To the complementary color firstprocessor 41, the first to fourth mixed pixel signals M1 to M4 (see FIG.10) are inputted from the complementary color type imaging device 28.The complementary color first processor 41 produces a luminance signal Yand color difference signals Cr and Cb by performing a well-known Y/Cconversion used in the complementary-color checkered-patterncolor-difference line sequential method, and then converts the luminancesignal Y and the color difference signals Cr and Cb into the RGB signalby a matrix operation. This RGB signal is sent to the channel allocator38. More specifically, the luminance signal Y and the color differencesignals Cr and Cb are calculated by addition and subtraction of thefirst mixed pixel signal M1 and the second mixed pixel signal M2 next toeach other in the row direction and addition and subtraction of thethird mixed pixel signal M3 and the fourth mixed pixel signal M4 next toeach other in the row direction.

The complementary color second processor 42 is chosen in a case wherethe endoscope 13 is of the complementary color type and the observationmode is the narrowband light observation mode. As shown in FIG. 15, thecomplementary color second processor 42 has a signal extractor 46, aninterpolator 47, and a mixed color corrector 48.

The signal extractor 46 extracts only the first and second mixed pixelsignals M1 and M2 out of the first to fourth mixed pixel signals M1 toM4 inputted from the complementary color type imaging device 28, andinputs the first and second mixed pixel signals M1 and M2 to theinterpolator 47. The interpolator 47 performs a well-known pixelinterpolation processing, to produce two signals of the first and secondmixed pixel signals M1 and M2 in the position of each mixed pixel. Themixed color corrector 48 performs mixed color correction processing byusing the following expression (3):

$\begin{matrix}{\begin{pmatrix}{M\; 1^{\prime}} \\{M\; 2^{\prime}}\end{pmatrix} = {\begin{pmatrix}1 & {- K_{2}} \\{- K_{1}} & 1\end{pmatrix}\begin{pmatrix}{M\; 1} \\{M\; 2}\end{pmatrix}}} & (3)\end{matrix}$

wherein, K₁ represents the ratio (M2 v/M1 v) of a second mixed pixelsignal M2 v to a first mixed pixel signal M1 v obtained in independentapplication of only the violet narrowband light Vn. K₂ represents theratio (M1 g/M2 g) of a first mixed pixel signal M1 g to a second mixedpixel signal M2 g obtained in independent application of only the greennarrowband light Gn.

The mixed color corrector 48 calculates correction coefficients K₁ andK₂ with the use of the first mixed pixel signals M1 v and M1 g and thesecond mixed pixel signals M2 g and M2 v obtained in the abovecalibration mode. The mixed color corrector 48 keeps holding thecalculated correction coefficients K₁ and K₂ until the calibration isperformed again.

The correction coefficients K₁ and K₂ may be obtained in the course ofmanufacture and stored to the information storage 30 of thecomplementary color type endoscope 13 a, and the main controller 31 mayobtain the correction coefficients K₁ and K₂ from the informationstorage 30 at the time when the complementary color type endoscope 13 ais connected to the light source device 11 and the processor device 12.Furthermore, if the calibration is performed, the correctioncoefficients K₁ and K₂ stored in the information storage 30 of thecomplementary color type endoscope 13 a are preferably deleted andreplaced with the correction coefficients K₁ and K₂ newly calculated bythe mixed color corrector 48.

The mixed color correction processing according to the expression (3)lowers a mixed color component (a green narrowband light Gn component inthe first mixed pixel signal M1 and a violet narrowband light Vncomponent in the second mixed pixel signal M2). The first and secondmixed pixel signals M1′ and M2′ after the mixed color correction aresent to the channel allocator 38.

The primary color first processor 43 is chosen in a case where theendoscope 13 is of the primary color type and the observation mode isthe normal light observation mode. To the primary color first processor43, the RGB signal is inputted from the primary color type imagingdevice 29. In this RGB signal, one of R, G, and B signals is assigned toeach pixel. The primary color first processor 43 produces three signalsof R, G, and B for each pixel by performing well-known pixelinterpolation processing. The RGB signals produced by the pixelinterpolation processing are sent to the channel allocator 38.

The primary color second processor 44 is chosen in a case where theendoscope 13 is of the primary color type and the observation mode isthe narrowband light observation mode. To the primary color secondprocessor 44, the RGB signal is inputted from the primary color typeimaging device 29. The primary color second processor 44 extracts a Bsignal for sensing the violet narrowband light Vn and a G signal forsensing the green narrowband light Gn, and produces a B signal and a Gsignal of each pixel by applying the pixel interpolation processing aswith above. The B signal and the G signal are sent to the channelallocator 38.

In the normal light observation mode, the channel allocator 38 receivesthe RGB signals irrespective of the type of the endoscope 13, and henceallocates the R, G, and B signals to an R channel, a G channel, and a Bchannel of the image display device 14, respectively. Therefore, thenormal image, that is, an image of the observation object irradiatedwith the normal light is displayed on the image display device 14.

In a case where the endoscope 13 is of the complementary color type andthe narrowband light observation mode is chosen, the channel allocator38 assigns the first and second mixed pixel signals M1′ and M2′ inputtedfrom the complementary color second processor 42 to the channels of theimage display device 14 as indicated by the following expression (4):

$\begin{matrix}{\begin{pmatrix}{Rch} \\{Gch} \\{Bch}\end{pmatrix} = {\begin{pmatrix}0 & 1 \\1 & 0 \\1 & 0\end{pmatrix}\begin{pmatrix}{M\; 1^{\prime}} \\{M\; 2^{\prime}}\end{pmatrix}}} & (4)\end{matrix}$

Therefore, an image of the observation object irradiated with the violetnarrowband light Vn and the green narrowband light Gn is displayed asthe special image on the image display device 14. Since the expression(4) assigns the first mixed pixel signal M1′ corresponding to the violetnarrowband light Vn to the two channels, the special image is such animage in which the structure of the superficial blood vessels (bloodcapillary) and the like in the vicinity of the surface of a living bodyis easily visible. Note that, the first and second mixed pixel signalsM1′ and M2′ may be weighted by coefficients other than “0” or “1” inassignment to the channels.

Furthermore, provided that the endoscope 13 is of the primary color typeand the narrowband light observation mode is chosen, the channelallocator 38 assigns the B signal and the G signal inputted from theprimary color second processor 44 to the channels of the image displaydevice 14 as indicated by the following expression (5):

$\begin{matrix}{\begin{pmatrix}{Rch} \\{Gch} \\{Bch}\end{pmatrix} = {\begin{pmatrix}0 & 1 \\1 & 0 \\1 & 0\end{pmatrix}\begin{pmatrix}B \\G\end{pmatrix}}} & (5)\end{matrix}$

Thus, an image of the observation object irradiated with the violetnarrowband light Vn and the green narrowband light Gn is displayed asthe special image on the image display device 14. This special image issuch an image in which the structure of the superficial blood vesselsand the like in the vicinity of the surface of the living body is easilyvisible. In a like manner, the B signal and the G signal may be weightedby coefficients other than “0” or “1” in assignment to the channels.

Next, a method for obtaining the expression (1), which determines theconfines of the light amount ratio Z, will be described. The first andsecond mixed pixel signals M1 and M2 are represented by the followingexpression (6), wherein “X” and “Y” represent the light amounts of theviolet narrowband light Vn and the green narrowband light Gn,respectively, simultaneously applied from the complementary color typeendoscope 13 a to the observation object, and “a₁” represents averagesensitivity of the first mixed pixels (Mg+Cy) to the violet narrowbandlight Vn, and “b₁” represents average sensitivity of the first mixedpixels (Mg+Cy) to the green narrowband light Gn, and “a₂” representsaverage sensitivity of the second mixed pixels (G+Ye) to the greennarrowband light Gn, and “b₂” represents average sensitivity of thesecond mixed pixels (G+Ye) to the violet narrowband light Vn. Theaverage sensitivity refers to an average of sensitivity in thewavelength band of each type of narrowband light.

$\begin{matrix}{\begin{pmatrix}{M\; 1} \\{M\; 2}\end{pmatrix} = {\begin{pmatrix}a_{1} & b_{1} \\b_{2} & a_{2}\end{pmatrix}\begin{pmatrix}X \\Y\end{pmatrix}}} & (6)\end{matrix}$

Using the sensitivity a₁, b₁, a₂, b₂, the correction coefficients K₁ andK₂ used in the above mixed color correction processing are representedby the following expressions (7) and (8).

$\begin{matrix}{K_{1} = {\frac{M\; 2v}{M\; 1v} = \frac{b_{2}}{a_{1}}}} & (7) \\{K_{2} = {\frac{M\; 1g}{M\; 2g} = \frac{b_{1}}{a_{2}}}} & (8)\end{matrix}$

By applying the mixed color correction represented by the expression (3)to the first and second mixed pixel signals M1 and M2 represented by theexpression (6), first and second mixed pixel signals M1′ and M2′ afterthe mixed color correction are represented by the following expressions(9) and (10).

$\begin{matrix}{{M\; 1^{\prime}} = {{( {a_{1} - \frac{b_{1}b_{2}}{a_{2}}} )X} = {( {1 - {K_{1}K_{2}}} )a_{1}X}}} & (9) \\{{M\; 2^{\prime}} = {{( {a_{2} - \frac{b_{1}b_{2}}{a_{1}}} )Y} = {( {1 - {K_{1}K_{2}}} )a_{2}Y}}} & (10)\end{matrix}$

Thus, the following expression (11) represents a condition of the lightamount ratio Z (=X/Y) that makes the light amount X of the violetnarrowband light Vn higher than the light amount Y of the greennarrowband light Gn applied simultaneously to the observation object(X>Y), and makes the signal value M2′ of the second mixed pixel used forimaging the green narrowband light Gn higher than the signal value M1′used for imaging the violet narrowband light Vn (M1′<M2′).

$\begin{matrix}{1 < Z < \frac{a_{2}}{a_{1}}} & (11)\end{matrix}$

The first mixed pixel signal M1 v obtained in independent application ofonly the violet narrowband light Vn of the light amount X_(i) isrepresented by the following expression (12). The second mixed pixelsignal M2 g obtained in independent application of only the greennarrowband light Gn of the light amount Y_(i) is represented by thefollowing expression (13):M1v=a ₁ X _(i)  (12)M2g=a ₂ Y _(i)  (13)

Substituting the expressions (12) and (13) into the expression (11)brings the above expression (1). Referring to FIG. 12, a₁≈0.45 anda₂≈0.98, so these values are substituted into the expression (11). Thus,the light amount ratio Z defined by the expression (1) is in theconfines of 1<Z<2.2, and the optimal light amount ratio Z₀ isapproximately 1.6.

FIG. 16 shows a ratio P1 (=a₁X/(a₁X+b₁Y)) of the violet narrowband lightVn component in the first mixed pixel signal M1, a ratio P2(=a₂Y/(a₂Y+b₂X)) of the green narrowband light Gn component in thesecond mixed pixel signal M2, and the sum (P1+P2) of the ratios P1 andP2, with respect to the light amount ratio Z (=X/Y). Wherein, a₁≈0.45,a₂≈0.98, b₁≈0.53, and b₂≈0.07 based on the spectral sensitivitycharacteristics of FIG. 12.

In the confines of the light amount ratio Z of 1<Z<2.2, the ratio P1increases while the ratio P2 decreases, relative to a value at Z=1.However, an increase rate of the ratio P1 is larger than a decrease rateof the ratio P2, so the sum of the ratios P1 and P2 increases (i.e. anS/N ratio increases). Therefore, in this confines, the colorseparability between the violet narrowband light Vn component and thegreen narrowband light Gn component is improved, and the signal valueM2′ of the second mixed pixel used for imaging the green narrowbandlight Gn is increased more than the signal value M1′ of the first mixedpixel used for imaging the violet narrowband light Vn. The greennarrowband light Gn is easily reflected by the mucosa membrane and thelike, though most of the violet narrowband light Vn is absorbed byhemoglobin in the superficial blood vessels. Therefore, M2′>M1′translates into increase in the light amount of the reflected light fromthe mucosa membrane and the like, and hence improvement in thevisibility of the superficial blood vessels (the contrast between thesuperficial blood vessels and the mucosa membrane).

Next, the operation of the endoscope system 10 will be described withreferring to a flowchart of FIG. 17. Upon connecting the endoscope 13 tothe light source device 11 and the processor device 12, the maincontroller 31 of the processor device 12 reads the specific informationfrom the information storage 30 of the endoscope 13 to judge whether theconnected endoscope is the complementary color type endoscope 13 a orthe primary color type endoscope 13 b. For example, in the case of thecomplementary color type endoscope 13 a, the main controller 31 puts thelight source device 11 and the processor device 12 into the normal lightobservation mode, and makes the selector 40 select the complementarycolor first processor 41 in the signal processing unit 37.

In the normal light observation mode, the dichroic mirror 22 isretracted to a position illustrated by a dotted line in FIG. 5 in theoptical combiner 24 of the light source device 11, and the WL-LED 20 bis turned on. The normal light (white light) WL from the WL-LED 20 b issupplied to the light guide 27 of the complementary color type endoscope13 a. Also, the complementary color type imaging device 28 of thecomplementary color type endoscope 13 a is driven by the imagingcontroller 32 by the field readout method, and outputs the first tofourth mixed pixel signals M1 to M4. The first to fourth mixed pixelsignals M1 to M4 are subjected to the Y/C processing and converted intothe RGB signal in the complementary color first processor 41, anddisplayed on the image display device 14 through the channel allocator38. Thus, the normal image captured under the normal light is displayedon the image display device 14.

The insert section 16 of the complementary color type endoscope 13 a isintroduced into a patient's body cavity to perform endoscopy. To inspectthe pattern of the superficial blood vessels and the like in tissue tobe inspected such as a lesion inside the body cavity, the mode switch 17a is operated. The main controller 31 detects the operation signal ofthe mode switch 17 a, and the light source device 11 and the processordevice 12 are put into the narrowband light observation mode.

In the narrowband light observation mode, the selector 40 selects thecomplementary color second processor 42 and the setting of the lightsource device 11 is changed. To be more specific, the dichroic mirror 22is disposed at the intersection point of the optical axes of the V-LED20 a and the WL-LED 20 b in the optical combiner 24. At this time, themain controller 31 controls the light source device 21 based on theoptimal light amount ratio Z₀ contained in the specific information readout of the information storage 30 so as to change the intensity ratiobetween the V-LED 20 a and the WL-LED 20 b, such that the violetnarrowband light Vn and the green narrowband light Gn exit from thecomplementary color type endoscope 13 a at the light amount ratio Zsatisfying the above expression (1).

The V-LED 20 a and the WL-LED 20 b are simultaneously turned on, and theviolet narrowband light Vn and the green narrowband light Gn are mixedin the optical combiner 24. The mixed narrowband light is supplied tothe light guide 27 of the complementary color type endoscope 13 a. Thecomplementary color type imaging device 28 is driven by the fieldreadout method, and outputs the first to fourth mixed pixel signals M1to M4. In the complementary color second processor 42, the signalextractor 46 extracts the first and second mixed pixel signals M1 and M2from the first to fourth mixed pixel signals M1 to M4. Then, theinterpolator 47 applies the pixel interpolation processing to the firstand second mixed pixel signals M1 and M2, and the mixed color corrector48 applies the mixed color correction to the first and second mixedpixel signals M1 and M2 and outputs the corrected first and second mixedpixel signals M1′ and M2′. The channel allocator 38 assigns the secondmixed pixel signal M2′ to the R channel and assigns the first mixedpixel signal M1′ to the G channel and the B channel, so the first andsecond mixed pixel signals M1′ and the M2′ are displayed on the imagedisplay device 14. Therefore, the special image captured under thenarrowband light is displayed on the image display device 14.

Since the violet narrowband light Vn is transmittable from the surfaceof the observation object to a first transmission distance in thevicinity of a superficial layer, a first image, which is based on theviolet narrowband light Vn, contains much of an image of structure atthe first transmission distance, such as the superficial blood vessels.This first image is produced based on the first mixed pixel signal M1.On the other hand, since the green narrowband light Gn is transmittablefrom the surface of the observation object to a second transmissiondistance in the vicinity of a middle to deep layer, a second image,which is based on the green narrowband light Gn, contains much of animage of structure at the second transmission distance, such as middleto deep blood vessels. The second image has high visibility of a minutepattern and the like of the mucosa membrane. This second image isproduced based on the second mixed pixel signal M2. The first image andthe second image are combined into the special image.

According to this embodiment, the light amount ratio Z is set based onthe optimal light amount ratio Z₀ so as to satisfy the expression (1)(preferably, set at Z=Z₀). Therefore, it is possible to obtain thespecial image that has improved color separability and improvedvisibility of the superficial blood vessels (improved contrast betweenthe superficial blood vessels and the mucosa membrane).

The special image is repeatedly displayed until the mode switch 17 a isoperated or completion operation for completing the endoscopy isperformed from the input device 15. Upon operating the mode switch 17 a,the endoscope system 10 is put back into the normal observation mode.The completion operation ends the operation.

On the other hand, in a case where the main controller 31 judges thatthe primary color type endoscope 13 b is connected to the light sourcedevice 11 and the processor device 12, the light source device 11 andthe processor device 12 are put into the normal light observation mode,and the selector 40 selects the primary color first processor 43. In thenormal light observation mode, as in the case of the complementary colortype, the normal light (white light) WL is produced by the light sourcedevice 11 and supplied to the light guide 27 of the primary color typeendoscope 13 b.

In this case, the primary color type imaging device 29 is driven by theprogressive readout method and outputs the RGB signal. This RGB signalis subjected to the pixel interpolation processing and the like in theprimary color first processor 43, and displayed on the image displaydevice 14 through the channel allocator 38. Thus, the normal imagecaptured under the normal light is displayed on the image display device14.

After that, upon operating the mode switch 17 a, the light source device11 and the processor device 12 are put into the narrowband lightobservation mode. In the narrowband light observation mode, the selector40 selects the primary color second processor 44, and the setting of thelight source device 11 is changed so that the dichroic mirror 22 isdisposed at the intersection point of the optical axes of the V-LED 20 aand the WL-LED 20 b in the optical combiner 24. In this case, incontrast to the complementary color type, the light emission intensityratio between the V-LED 20 a and the WL-LED 20 b is set so as to satisfyZ=1. The narrowband light, being the mixture of the violet narrowbandlight Vn and the green narrowband light Gn, is produced and supplied tothe light guide 27 of the primary color type endoscope 13 b.

The primary color type imaging device 29 is driven by the progressivereadout method and outputs the RGB signal. Out of the RGB signal, theprimary color second processor 44 extracts only the B signal and the Gsignal. The B signal and the G signal are subjected to the pixelinterpolation processing and the like, and displayed on the imagedisplay device 14 through the channel allocator 38. Thus, the specialimage captured under the narrowband light is displayed on the imagedisplay device 14.

As in the case of the complementary color type, the special image isdisplayed repeatedly until the mode switch 17 a is operated or thecompletion operation is performed from the input device 15. Uponoperating the mode switch 17 a, the endoscope system 10 is put back intothe normal observation mode. The completion operation ends theoperation.

In a case where the complementary color type endoscope 13 a is connectedto the light source device 11 and the processor device 12, thecalibration for recalculating the optimal light amount ratio Z₀ can beperformed by operation of the input device 15 or the like. In thecalibration, a white plate or the like is used as an object to beimaged.

In the calibration, the selector 40 selects the calibration processor45, and the violet narrowband light Vn and the green narrowband light Gnare applied at the currently used light amount ratio Z in a time sharingmanner. The complementary color type imaging device 28 outputs the firstmixed pixel signals M1 v and M1 g and the second mixed pixel signals M2g and M2 v, and the calibration processor 45 calculates an average ofeach signal value. Then, the optimal light amount ratio calculator 39calculates the optimal light amount ratio Z₀ based on the currently usedlight amount ratio Z and the average value of each of the first andsecond mixed pixel signals M1 v and M2 g. The main controller 31 setsthe calculated optimal light amount ratio Z₀ to the light source device11, and deletes and replaces the optimal light amount ratio Z₀ stored inthe information storage 30 of the complementary color endoscope 13 a.

The first mixed pixel signals M1 v and M1 g and the second mixed pixelsignals M2 g and M2 v obtained in the calibration are used forcalculating the correction coefficients K₁ and K₂. The calculatedcorrection coefficients K₁ and K₂ are written to the information storage30 of the complementary color type endoscope 13 a and used in the nextuse of the complementary color type endoscope 13 a.

Note that, the light amount ratio Z is set by regulating the lightemission intensity of the V-LED 20 a and the WL-LED 20 b in the aboveembodiments, but may be set by regulating light emission time.Furthermore, both of the light emission intensity and the light emissiontime may be regulated in order to set the light amount ratio Z.

The LED light source 20 contains the V-LED 20 a and the WL-LED 20 b inthe above embodiment, but a blue LED, which emits blue narrowband lightBn having a wavelength band on a longer side than the violet narrowbandlight Vn, as shown in FIG. 18, may be used instead of the V-LED 20 a.The center wavelength of the blue narrowband light Bn is within theconfines of approximately 410 nm to 420 nm, and preferably atapproximately 415 nm.

Instead of the V-LED 20 a and the WL-LED 20 b, a plurality of LEDs (forexample, four LEDs) having different emission wavelength bands may beprovided. Turning on all the LEDs produces the normal light (whitelight), while turning on two of the LEDs produces two types ofnarrowband light. Furthermore, another type of semiconductor lightsource such as an LD (laser diode) may be used instead of the LED.

Another light source device that has a lamp for emitting light having awide wavelength band such as white light and a narrowband filter may beused instead of the light source device 11 described in the aboveembodiment. In FIG. 19, a light source device 60 includes a lamp 61, aninfrared cut filter 62, an aperture stop 63, an aperture driver 64, arotary filter unit 65, a filter switcher 66, and a condenser lens 67.

The lamp 61 emits white light WL under the control of the above maincontroller 31. The infrared cut filter 62 cuts an infrared component outof the white light WL produced by the lamp 61, so the remainingcomponent enters the aperture stop 63. The aperture driver 64 regulatesthe opening size of the aperture stop 63 to adjust the transmissionlight amount of the white light WL. This aperture driver 64 iscontrolled by the dimmer 36 described above.

As shown in FIG. 20, the rotary filter unit 65 has a first narrowbandfilter 65 a, a second narrowband filter 65 b, and an opening 65 c. Thefilter switcher 66 turns the rotary filter unit 65 under the control ofthe main controller 31, so that one of the first narrowband filter 65 a,the second narrowband filter 65 b, and the opening 65 c is disposed inan optical axis of the white light WL.

As shown in FIG. 21, the first narrowband filter 65 a is a two-peakfilter, which has a first characteristic section Va having a band-passcharacteristic at a first narrowband (a center wavelength of 405 nm) anda second characteristic section Ga having a band-pass characteristic ata second narrowband (a center wavelength of 540 nm). The firstcharacteristic section Va and the second characteristic section Ga haveapproximately equal transmittance.

This first narrowband filter 65 a is disposed in the optical axis of thewhite light WL, in a case where the narrowband light observation mode ischosen and the endoscope 13 is of the primary color type. Passing thewhite light WL through the first narrowband filter 65 a produces theviolet narrowband light Vn and the green narrowband light Gn. The violetnarrowband light Vn and the green narrowband light Gn enter the lightguide 27 through the condenser lens 67. The light guide 27 has thespectral attenuation characteristic as shown in FIG. 13. Thetransmittance of the first characteristic section Va may be set a littlehigher than the transmittance of the second characteristic section Ga inconsideration of the spectral attenuation characteristic and the like,so as to substantially equalize the light amounts of the violetnarrowband light Vn and the green narrowband light Gn exiting from thelight guide 27.

As shown in FIG. 22, the second narrowband filter 65 b is a two-peakfilter that has a first characteristic section Vb having a band-passcharacteristic in a first narrowband and a second characteristic sectionGb having a band-pass characteristic in a second narrowband. The firstcharacteristic section Vb and the second characteristic section Gb havemuch different transmittance.

This second narrowband filter 65 b is disposed in the optical axis ofthe white light WL, in a case where the narrowband light observationmode is chosen and the endoscope 13 is of the complementary color type.Passing the white light WL through the second narrowband filter 65 bproduces the violet narrowband light Vn and the green narrowband lightGn having a predetermined light amount ratio corresponding to thetransmittance ratio between the first and second characteristic sectionsVb and Gb. The violet narrowband light Vn and the green narrowband lightGn enter the light guide 27 through the condenser lens 67. Thetransmittance ratio between the first and second characteristic sectionsVb and Gb is set in consideration of the spectral attenuationcharacteristic of the light guide 27 and the like, such that the lightamount ratio Z between the violet narrowband light Vn and the greennarrowband light Gn exiting from the light guide 27 satisfies theexpression (1) (preferably, Z=Z₀).

The opening 65 c is disposed in the optical axis of the white light WLin a case where the normal observation mode is chosen. The opening 65 cpasses the white light WL incident thereon as-is without limiting itswavelength. The white light WL enters the light guide 27 through thecondenser lens 67, and exits from the light guide 27 as the normallight.

The above embodiments use the complementary color type imaging device 28having the complementary color type color separation filter 28 a of thecomplementary-color checkered-pattern color-difference line sequentialmethod, as shown in FIG. 7, but may use another complementary color typeimaging device having another complementary color type color separationfilter, as shown in FIG. 23, of the complementary-colorcheckered-pattern color-difference line sequential method, instead.

In the above embodiments, the combination of the Mg pixel and the Cypixel composes the first mixed pixel, and the combination of the G pixeland the Ye pixel composes the second mixed pixel. However, thecombinations of mixed pixels are not limited to these and arbitrarilychangeable.

According to the above embodiments, in the calibration mode, the violetnarrowband light Vn and the green narrowband light Gn are applied at thecurrently used light amount ratio Z in a time-sharing manner, and theoptimal light amount ratio Z₀ is calculated based on this light amountratio Z and the signal values of the first and second mixed pixels.Instead of this, the violet narrowband light Vn and the green narrowbandlight Gn may be applied with stepwise change of the light amount ratio Zin a time-sharing manner, and the magnitude relation between the signalvalue M1′ of the first mixed pixel and the signal value M2′ of thesecond mixed pixel obtained at each light amount ratio Z may be judged,in order to determine the confines corresponding to the expression (1)and the optimal light amount ratio Z₀ corresponding to the expression(2).

According to the above embodiments, the imaging controller 32, the CDScircuit 33, the A/D converter 34, and the like are contained in theprocessor device 12, but may be provided in the endoscope 13.

In the above embodiments, the complementary color type imaging device 28and the primary color type imaging device 29 are constituted of the CCDimage sensors, but may be constituted of CMOS image sensors. In the caseof the CMOS image sensor, the imaging controller 32, the CDS circuit 33,the A/D converter 34, and the like are formable in a CMOS semiconductorsubstrate formed with the image sensor.

According to the above embodiments, both of the complementary color typeendoscope and the primary color type endoscope are connectable to thelight source device and the processor device, but only the complementarycolor type endoscope may be connectable thereto.

In the above embodiments, the light source device and the processordevice are configured as independent devices, but may be formed into asingle device. Furthermore, the light source device may be incorporatedin the endoscope.

Note that, “lighting section” described in claims corresponds to acombination of “light source device” and “optical members (light guide,lighting lens, and the like) for leading light from the light sourcedevice and applying the light to an observation object” described in theembodiments.

Although the present invention has been fully described by the way ofthe preferred embodiment thereof with reference to the accompanyingdrawings, various changes and modifications will be apparent to thosehaving skill in this field. Therefore, unless otherwise these changesand modifications depart from the scope of the present invention, theyshould be construed as included therein.

What is claimed is:
 1. An endoscope system comprising: a complementarycolor type endoscope including a complementary color type imaging devicehaving pixels to each of which one of color filter segments of cyan,magenta, yellow and green is attached; a lighting section having a lightsource device for generating first narrowband light having a centerwavelength in a blue or violet wavelength range and second narrowbandlight having a center wavelength in a green wavelength range, saidcomplementary color type endoscope being detachably connected to saidlight source device; and a controller for setting a first light amountratio at a value more than 1, said first light amount ratio being alight amount ratio of a light amount of said first narrowband light to alight amount of said second narrowband light in case of saidcomplementary color type endoscope being connected to said light sourcedevice, wherein said complementary color type endoscope and a primarycolor type endoscope having a primary color type imaging device aredetachably connected to said light source device, and wherein saidcontroller sets said first light amount ratio at a value more than avalue of a second light amount ratio, said second light amount ratiobeing a light amount ratio of a light amount of said first narrowbandlight to a light amount of said second narrowband light in case of saidprimary color type endoscope being connected to said light sourcedevice.
 2. The endoscope system according to claim 1, wherein saidlighting section simultaneously applies said first narrowband light andsaid second narrowband light to an observation object.
 3. The endoscopesystem according to claim 1, wherein a first mixed pixel and a secondmixed pixel are read out from said complementary color type imagingdevice, each of said first mixed pixel and said second mixed pixelsensing both of said first narrowband light and said second narrowbandlight, said endoscope system further comprises a signal processing unitfor imaging said first narrowband light by using a signal value of saidfirst mixed pixel, and imaging said second narrowband light by using asignal value of said second mixed pixel, and said controller sets saidfirst light amount ratio such that a signal value of said second mixedpixel is made higher than a signal value of said first mixed pixel. 4.The endoscope system according to claim 1, further comprising an imagedisplay device having an R channel, a G channel and a B channel, asignal corresponding to said first narrowband light being assigned tosaid G channel and said B channel.
 5. The endoscope system according toclaim 1, wherein said light source device includes a plurality of LEDlight sources, and said controller sets said first light amount ratio byregulating at least one of light emission intensity and light emissiontime of said plurality of LED light sources.
 6. An endoscope systemcomprising: a complementary color type endoscope including acomplementary color type imaging device having pixels to each of whichone of color filter segments of cyan, magenta, yellow and green isattached; a lighting section having a light source device for generatingfirst narrowband light having a center wavelength in a blue or violetwavelength range and second narrowband light having a center wavelengthin a green wavelength range, said complementary color type endoscopebeing detachably connected to said light source device; and a controllerfor setting a first light amount ratio at a value more than 1, saidfirst light amount ratio being a light amount ratio of a light amount ofsaid first narrowband light to a light amount of said second narrowbandlight in case of said complementary color type endoscope being connectedto said light source device, wherein a first mixed pixel and a secondmixed pixel are read out from said complementary color type imagingdevice, said first mixed pixel being a combination of a magenta pixeland a cyan pixel, said second mixed pixel being a combination of a greenpixel and a yellow pixel, each of said first mixed pixel and said secondmixed pixel sensing both of said first narrowband light and said secondnarrowband light, and sensitivity of said second mixed pixel to saidsecond narrowband light being higher than sensitivity of said firstmixed pixel to said first narrowband light, said endoscope systemfurther comprises a signal processing unit for imaging said firstnarrowband light by using a signal value of said first mixed pixel, andimaging said second narrowband light by using a signal value of saidsecond mixed pixel, and said controller sets said first light amountratio such that a signal value of said second mixed pixel is made higherthan a signal value of said first mixed pixel.